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1 2005

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Complexes of Adenine with Metal Ions: Stability and Excited States

Rubina A., Rubin Y., Sorokin V., Shukla M., Leszczyński J.

Polish Journal of Chemistry

2005

Vol. 79 / nr 12

1873-1882

Molecular geometry optimizations and excited state energy calculations were performed for the N9H and N7H tautomers of adenine (Ade) and their complexes with selected transition metal ions (Cu+, Cu2+, Zn2+ and Ag+). The ground state geometry optimizations were carried out at the HF and UHF (for open-shell metal ions) levels, while transition energies were calculated using the configuration interaction involving single excited configurations (CIS method). Single point ground state energy calculations were also performed at the full MP2 (UMP2 for open-shell systems) level. The 6-31+G(d,p) basis set was used for all but Ag+ containing complexes for which the LANL2DZ basis set was used. Experimental UV-spectra of adenine complexes with Cu2+ and Ag+ metal cations in the water solution were also obtained. These spectra show red-shift of approximately 1000 cm-1 in comparison with that of the adenine. The analysis of the first electronic singlet - * transition energies suggests that metal ion binding to the N1 or N7 atomic sites of adenine generally leads to the red-shift, while the binding at the N9 site leads to blue shift of the absorption maximum of complexes. The most probable binding site for the Cu+ and Zn2+ ions is found to be the N7 atomic site of the N9H tautomer of adenine. Divalent copper Cu2+ ion would bind at the N1 site. Co-existence of the two forms of adenine complexes with silver ion ([N9H-Ade-AgN1]+, and [N9H-Ade-AgN7]+) is also revealed.